Different industrial gases produced with a view to being used in organic synthesis, such as the gases resulting from the gasification of coal that can be used in the methanation reactions or hydrogen sulfide used in the chemical industry for the synthesis of thioorganic products contain, depending on the methods by which they were obtained, more or less large quantities of COS and/or CS.sub.2. These organic sulfur compounds are generally undesireable for the synthesis reaction in which industrial gases take part, since they can poison the catalysts used to promote such reactions.
Prior to using in synthesis an industrial gas containing COS and/or CS.sub.2 impurities, it is necessary to subject that gas to a very complicated purification in order to eliminate the sulfur compounds.
The purification techniques by washing with regenerable selective liquid absorbent such as an amine solution, which are usually utilized for eliminating H.sub.2 S contained in the gases, are not generally effective for eliminating COS and CS.sub.2, since these compounds are not absorbed by the absorbent liquid.
The COS and CS.sub.2 compounds could be eliminated by putting the gas to be purified in which they are contained in contact with a solid absorbent of the zinc oxide type that irreversibly fixes said compounds. This involves a considerable consumption of solid absorbent which makes such a purification method uneconomical and significantly reduces its attractiveness. Besides, it is not possible to use this method of purification when some of the essential components of the gas to be purified are likely to react with the solid absorbent, as is the case when the gas to be treated contains H.sub.2 S.
It is known that the gases treated in the catalytic converters of a sulfur unit contain small quantities of COS and CS.sub.2 together with a larger quantity of H.sub.2 S and SO.sub.2 reagents that take part in the CLAUS reaction for the formation of sulfur. Since a substantial quantity of water vapor of about 30% by volume is present, the COS and CS.sub.2 compounds undergo a partial hydrolysis in H.sub.2 S when in contact with the CLAUS catalyst present in the catalytic converters due to the high water vapor content of the treated gases. The hydrolysis is noticeable in the first converter where the temperature is about 350.degree. C. and negligible in the converters that follow where the temperature is lower.
In particular in European patent application published under No. 0060741, it is shown that when a catalyst containing TiO.sub.2 and a sulfate of an alkaline earth metal, is in contact with small concentrations of CS.sub.2 and COS compounds namely, 1% by volume for CS.sub.2 and 0.3% by volume for COS, in a gas containing more considerable quantities of H.sub.2 S and of CO.sub.2 and a substantial quantity of water vapor (28% by volume), that is, in a gas having substantially the composition of the gases treated in the first converter of a sulfur plant, the CS.sub.2 and COS are completely hydrolyzed in H.sub.2 S at a temperature of 340.degree. C. In the case of the hydrolysis of the CS.sub.2, example 10 of the above European patent application, the quantity of water vapor contained in the reaction mixture corresponds to a value of the molar ratio H.sub.2 O:CS.sub.2 equal to 28, while in the case of the hydrolysis of the COS, example 11 of the application, the quantity of water vapor present in the reaction mixture corresponds to a value of the molar ratio H.sub.2 O:COS equal to 93.